Police checked IDs and searched the bags of anyone seeking to enter the environs of the vast public space in the centre of the capital where thousands of students, workers and ordinary citizens gathered in 1989 to demand political reforms.
Journalists from The Associated Press were stopped, filmed and ultimately forced to leave the area, ostensibly for lacking proper permission.
Hundreds, possibly thousands, of people were killed as tanks and troops converged on Beijing on the night of June 3-4, 1989.
Memorials were planned in the semi-autonomous Chinese territory of Hong Kong and in self-governing Taiwan, where some former student leaders have found refuge.
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Ahead of the anniversary, family members of those killed in the crackdown were placed under additional restrictions, either confined to their homes or forced to leave the capital.
China's government has rejected their calls for an independent accounting of the events and those killed and maimed by soldiers.
At least half a dozen people have reportedly been detained in recent days for attempting to commemorate the events, although a small group wearing T-shirts condemning the crackdown converged on the square last Sunday.
In Washington, the US State Department called for a "full public accounting of those killed, detained, or missing and for an end to censorship of discussions about the events of June 4, 1989, as well as an end to harassment and detention of those who wish to peacefully commemorate the anniversary."
In a statement, it also urged the Chinese government to respect the rights and freedoms of all its citizens.
Asked yesterday about the anniversary, Chinese Foreign Ministry spokeswoman Hua Chunying said China had "long ago reached a clear conclusion about the political turmoil at the end of 1980s and other related issues."